18 
SIR WILLIAM CROOKES ON THE PREPARATION OF 
Glass 165. 
Raw soda flux. 87'56 
Cerium borate. 8'00 
Ferrous sulphate, crystallised. 3'00 
Uranic oxide. 0'55 
Nickel oxide. 0'09 
Chromic oxide .......... 0'80 
100'00 
This glass cuts off practically all the ultra-violet rays shorter than X3680, and 38 
per cent, of the heat radiation. It transmits 48 per cent, of the light. Its colour is 
a pale yellowish green. Its tintometer numbers are :—Yellow, 4'0 ; blue, 2'50. 
, Glass 187. 
This glass and the next are both cerium glasses. No. 187 is composed of:— 
Fused soda flux. 83'0 
Cerium nitrate, crystallised. 17'0 
lOO'O 
The heat rays cut off by this glass are only 27 per cent., but its other qualifications 
are important. It is practically opaque to ultra-violet radiation, the limit being 
X 3650, and it transmits 99 per cent, of the light. 
• In the tintometer and opacity meter no colour or want of transparency can be 
detected, although against white paper in a good light a faint tinge of yellow is 
perceptible. 
Glass 197. 
Fused soda flux. 79'00 
Cerium nitrate, crystallised. 2O'50 
Nickel sulphate, crystallised. 0'30 
Cobalt sulphate, crystallised. 0'05 
Uranoso-uranic oxide. 0'15 
lOO'OO 
Nickel and cobalt are here mixed in the proportion to make a neutral tinted glass, 
the other ingredients only slightly modifying the colour. The colour is a pale neutral. 
It is opaque to ultra-violet rays of shorter wave-length than X 3799, and cuts off 41 per 
cent, of the heat rays. It is transparent to 45 per cent, of the incident light. The 
numbers in the tintometer are :—Red, 2'00 ; yellow, 3'00 ; blue, 5'50, 
